A paper has been uploaded to Researchgate claiming: Carn Goedog on Mynydd Preseli was not the site of a bluestone megalith quarry
"This paper examines the hypothesis that Carn Goedog, a prominent tor on the north 5lank of Mynydd Preseli in Pembrokeshire, Wales, was the site of a Neolithic quarry from which Stonehenge bluestones were extracted on a large scale. The dolerite sills in the area are geochemically heterogenous, with multiple outcrops. Claims of !precise provenancing" of Stonehenge spotted dolerite fragments to Carn Goedog are questionable.. Geomorphological studies on the tor reveal that pillars suitable for use as monoliths are restricted to a few small areas, difficult to access. Frost-shattered blocks dominate. Many have sub-rounded edges, suggesting long-term weathering and redistribution by glacier ice. Moulded and smoothed surfaces indicate that the influence of overriding ice has been considerable. At Stonehenge, most of the bluestones are abraded boulders which look like glacial erratics. Examinations of the supposed !Neolithic quarry" site reveal that all of the "engineering features" are natural. Stone artefacts owe nothing to quarrying activities, but point to a history of intermittent occupation. Soft shale "wedges" supposedly used for extracting pillars from the rock face are natural and ubiquitous. Radiocarbon dating effectively falsifies the quarrying hypothesis. There was no Neolithic quarry at Carn Goedog, and if blocks of spotted dolerite were extracted and transported away from the vicinity of the tor, the agency was glacier ice." (sic)
That is probably all you need to read, no evidence that bluestones were transported by glaciers, presumably to Salisbury Plain, is offered.